BCH5413 EXAM 1 WITH QUESTIONS AND ANSWERS

In the experiment described that supports DNA as the genetic material: Why does the mouse die if the researcher mixes the complete dead pathogenic strain with live non-pathogenic strain bacteria and then inject it into the mouse? (The first mouse in the figure). - ANSWER The mouse dies because the R strain has been transformed and is now an S strain, capable of producing the virulence factors that make the S strain deadly to mice. This is because as the pathogenic strain is killed, its DNA is released, and now floating freely can go into the R strain and transform it. In the experiment described that supports DNA as the genetic material: What was the only scenario in which the mouse lives? Why? - ANSWER The only scenario in which the mouse lives is when DNA is destroyed. This is because it's DNA that contains the genetic information that codes for the virulence factors that kill mice when they become infected. In DNA, C1 is bonded to... This is important because... - ANSWER a nitrogenous base (adenine, guanine, cytosine, or thymine) Importance - this allows the nitrogenous bases to form hydrogen bonds (A-T, C-G) between the 5`-3` strand and the 3`-5` strand. In DNA, C2 is bonded to... This is important because... - ANSWER H Importance - C2 does not have a hydroxyl group, which distinguishes it from RNA. In DNA, C3 is bonded to... This is important because... - ANSWER OH Importance - The C3 of one sugar forms a phosphodiester bond with the 5` phosphate of another sugar. In DNA, C4 is bonded to... - ANSWER C5 In DNA, C5 is bonded to... This is important because... - ANSWER phosphate Importance - The C5 can be the lead sugar or form phosphodiester bonds with the C3 of a second sugar. This gives DNA the 5` to 3` linkage. Describe why DNA has directionality. - ANSWER The 5' end has a free phosphate group and 3' end has a free hydroxyl (OH) group. Nucleotide strands form hydrogen bonds between the nitrogenous base off the 1' Carbon. DNA is always synthesized in the 5'-to-3' direction, which means that nucleotides are added only to the 3' end of the growing strand. In DNA, G forms 3 hydrogen bonds to C, A forms two hydrogen bonds to T. Sequence of DNA has an effect on the structure. What is the meaning of the term antiparallel in the structure of DNA? - ANSWER Antiparallel in the structure of DNA refers to how each strand of the double helix is parallel to each other, but their orientation is opposite; their 5' - 3' polarities are in opposite directions. 5. What does the Meselson and Stahl experiment confirm? - ANSWER In 1958 Meselson and Stahl published their experiment of DNA replication in Escherichia coli. In this experiment they started their DNA molecule with heavy nitrogen bases and when they are separated the new strand made was with light nitrogen bases and the new daughter strand each was found to have one heavy and one light strand which proved the DNA replication mechanism as semiconservative DNA replication model as proposed by Watson and Crick. True/False: Most biological DNA is positively supercoiled. - ANSWER False, Biological DNA is negatively supercoiled True/False: GC rich DNA has a lower melting temperature than AT rich DNA - ANSWER False, GC rich DNA has a higher melting temperature because it forms 3 hydrogen bonds compared to the 2 hydrogen bonds by AT. True/False: Chargaff's rule: A=G and T=C - ANSWER False The rule is that DNA from any organism should have a stoichiometric relationship of 1:1 for pyrimidines : purines or stated mathematically C + T (pyrimidines) = A + G (purines). The number of pyrimidines (C, T) however does not need to be equal (C=T), or purines for that matter. True/False: Increased salt concentration increases the stability of complimentary base pairing - ANSWER True Does A DNA or Z DNA have a right handed helix? - ANSWER A DNA Does A DNA or Z DNA have 12 bp per turn? - ANSWER Z DNA Is A DNA or Z DNA the dehydrated form? - ANSWER A DNA Describe three differences between DNA and RNA. - ANSWER 1. The nitrogenous bases vary; for DNA the nitrogenous bases are Adenine, Thymine, Guanine and Cytosine whereas RNA nitrogenous bases are Adenine, Uracil, Guanine, and Cytosine 2. RNA has a hydroxyl group (-OH) on the 2' carbon of the 5-carbon sugar whereas DNA has a hydrogen (-H) (note: this is where the name *RIBOnucleic* acid and *DEOXYRIBOnucleic* acid comes from) 3. DNA is a double strand and has major and minor grooves whereas RNA is a single strand with only major grooves Describe similarities between DNA and RNA. - ANSWER 1. Both DNA and RNA are large biological polymers 2. Both DNA and RNA are nucleic acids 3.Both DNA and RNA consists of sugar, nitrogenous bases, and a phosphate backbone 4. On both molecules Guanine pairs with Cytosine 5. Both store genetic information What is the central dogma? Give two examples of RNAs that are exceptions to the central dogma. Why are they exceptions? - ANSWER Central dogma can be stated as a DNA → RNA → protein pathway. Some viral RNA is the exception to it. One RNA virus encodes RNA-dependent RNA polymerases (RdRPs) to replicate and transcript based on the RNA template. Another is also RNA viruses encode reverse transcriptase to synthesize DNA based on the information on the RNA template. What are the two functions of DNA in cells? - ANSWER Cellular DNA contains two functions. One is the passing of genetic information to daughter cells. The other is the storage of information for the creation of mRNA by the process of transcription. Diploid refers to... - ANSWER the presence of two complete sets of chromosomes in an organism's cells, with each parent contributing a chromosome to each pair. Humans are diploid and most of the body's cells contain 23 chromosome pairs. Allele - ANSWER one of two or more versions of DNA sequence (a single base or a segment of bases) at a given genomic location. An individual inherits two alleles, one from each parent, for any given genomic location where such variation exists. Heterozygous - ANSWER Having inherited different versions (alleles) of a genomic marker from each biological parent. An individual who is heterozygous for a genomic marker has two different versions of that marker. Meiosis - ANSWER a type of cell division in sexually reproducing organisms that reduces the number of chromosomes in gametes ( the sex cells, or egg and sperm). In humans, body (or somatic) cells are diploid, containing two sets of chromosomes (one from each parent). To maintain this state, the egg and sperm that unite during fertilization must be haploid, with a single set of chromosomes. During meiosis, each diploid cell undergoes two rounds of divisions to yield four haploid daughter cells which are gametes. What is the difference between and intron and an exon? - ANSWER Introns are non-coding sequences present in DNA and are removed before translation begins through RNA splicing. On the other hand, exons are gene coding sequences of DNA. Unlike introns, exons are present in mRNA. How can one stretch of DNA be used to create more than one protein? - ANSWER Once the DNA is transcribed to RNA, the introns are removed and some exons may be removed as well through a process known as splicing. Alternate splicing can give you different protein combinations due to the exons that are present, for example one protein can contain exon 1, 2, and 3 while another contains exon 1, 3 and 4. The protein that is created depends on the regulation of the splicing mechanism and what type of mechanism is being used. What is the meaning of the term exon shuffling? How is this process related to the development of new proteins? - ANSWER Exon shuffling is a molecular mechanism for the formation of new genes. It is a process in which two or more exons from different genes can be brought together ectopically or the same exon can be duplicated to create a new exon-intron structure. Exons can be shuffled and create